1. Field of the Invention
The present invention relates generally to fluid flow cells and, more particularly, to mechanisms for supplying different fluids to such cells. The invention is particularly advantageous for supplying a sample, and a wash or calibration solution to the entrance port of flow cells adapted to analyze the sample material.
2. Description of the Prior Art
U.S. Pat. No. 3,997,420, assigned to the assignee of the present invention, describes a flow cell for use in blood chemistry analyses and in particular for determining the pH, pCO.sub.2 and pO.sub.2 of blood. The cell employs pH, pCO.sub.2, and pO.sub.2 measuring electrodes mounted adjacent a sample passage extending through the cell. A blood sample is collected in a conventional syringe and the syringe plunger is actuated to drive the sample through the flow cell passage in contact with each of the measuring electrodes. A wash solution is then conveyed through the passage to discharge the remaining sample therefrom to prepare the flow cell for receipt of the next injected sample. In addition, a calibration solution or gas is periodically conveyed through the passage, as required, to calibrate the measuring electrodes.
In the foregoing apparatus a sample filled syringe is secured by a leur fitting to a rotatable disc in alignment with a passage through the disc, and the disc is rotated to align the passage and hence the syringe outlet with the entrance port of the flow cell passage. The disc makes frictional sliding contact with the entrance port in a plane perpendicular thereto and hence is subject to sample leakage at the sliding contact. Moreover, the wash and calibration solutions, are introduced into the flow cell passage at a point downstream of the flow cell entrance port through a complicated arrangement of valves and pumps. Consequently, the flow of wash solution bypasses the entrance port thus requiring that an operator flush the port to prevent clogging and contamination of the port by a prior sample and resulting carryover of such contamination into subsequently injected samples.